Sweep-type spectrum analyzers are widely utilized to examine the spectra of various types of signal, by directly displaying the relative amplitudes of the signal frequency components, usually upon a CRT display. In many cases it is desired to examine only a single part of the frequency span of a signal, i.e. a relatively narrow frequency range within which a peak signal level occurs. In the prior art, it has been generally necessary to search through a wide range of frequencies, manually adjusting control knobs while observing the CRT display, in order to find the desired peak level and to set the center frequency of the displayed frequency span to approximately correspond to the frequency at which the signal peak occurs. In addition, it is necessary to adjust the amplitude of the displayed signal peak to a suitable level, e.g. by some form of manually adjustable gain control. In certain applications, the amount of time required for such manual operations may be unacceptable, and there is therefore an urgent need for a spectrum analyzer which will perform such adjustments to display a peak signal level of a signal spectrum in a rapid and completely automatic manner.
In the prior art, various types of signal tracking functions have been proposed, to be incorporated into a spectrum analyzer. With such a signal tracking function, the user must first set the frequency sweep range, i.e. the frequency span, to cover a wide range of frequencies, and must find the desired peak signal level from the displayed spectrum thus generated on the CRT. The frequency of this peak level can then be adjusted to a suitable position on the display, i.e. such that the peak signal level appears at about the center of the display. Thereafter, as the user narrows the frequency span down to a desired value, to enable close examination of the range of frequencies around this peak level, the spectrum analyzer automatically holds the position of the displayed peak level fixed on the display, e.g. holds the center frequency of the displayed frequency span fixed at the frequency of the desired peak signal level.
A spectrum analyzer equipped with such a signal tracking feature is less time-consuming to use than a purely manual type of spectrum analyzer. However it is still necessary for the user to initially perform manual frequency adjustment such that the desired peak signal level will appear on the CRT display, and of course also to adjust the amplitude of the displayed peak level to a suitable value. In addition, the zero-beat component may be erroneously selected and made to appear on the display, instead of the desired peak level. There is therefore a requirement for a spectrum analyzer which will perform all of the adjustment operations described above in a purely automatic manner, with no manual operations other than actuation of a push-button. Such a spectrum analyzer is proposed by the present invention.